Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable medical device system. For example, the disclosed invention can also be used with a Bion™ implantable stimulator, such as is shown in U.S. Patent Publication 2007/0097719, filed Nov. 3, 2005, or with other implantable medical devices.
As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible device case 30 formed of titanium for example. The case 30 typically holds the circuitry and battery 26 necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102 and 104 are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112 and 114 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 102, labeled E1-E8, and eight electrodes on lead 104, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary. The leads 102, 104 couple to the IPG 100 using lead connectors 38a and 38b, which are fixed in a header material 36, which can comprise an epoxy for example.
As shown in FIG. 2, the IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB 16. Two coils are generally present in the IPG 100: a telemetry coil 13 used to transmit/receive data to/from an external controller 12; and a charging coil 18 for charging or recharging the IPG's battery 26 using an external charger 50. The telemetry coil 13 can be mounted within the header 36 of the IPG 100 as shown.
As just noted, an external controller 12, such as a hand-held programmer or a clinician's programmer, is used to send data to and receive data from the IPG 100. For example, the external controller 12 can send programming data to the IPG 100 to dictate the therapy the IPG 100 will provide to the patient. Also, the external controller 12 can act as a receiver of data from the IPG 100, such as various data reporting on the IPG's status. The external controller 12, like the IPG 100, also contains a PCB 70 on which electronic components 72 are placed to control operation of the external controller 12. A user interface 74 similar to that used for a computer, cell phone, or other hand held electronic device, and including touchable buttons and a display for example, allows a patient or clinician to operate the external controller 12.
Wireless data transfer between the IPG 100 and the external controller 12 takes place via inductive coupling. To implement such functionality, both the IPG 100 and the external controller 12 have telemetry coils 13 and 17. Either coil can act as the transmitter or the receiver, thus allowing for two-way communication between the two devices, as explained further below. When data is to be sent between the external controller 12 and the IPG 100, the transmitting coil 17 or 13 is energized with alternating current (AC), which generates a magnetic field 29, which in turn induces a current in the other of coils 17 or 13. The generated magnetic field 29 is typically modulated using a communication protocol, such as a Frequency Shift Keying (FSK) protocol, which is well known in the art. The power used to energize the coil 17 or 13 can come from batteries 76 and 26 within the external controller 12 and IPG 100 respectively. The induced current in the receiving coil can then be demodulated back into the telemetered data signals.
The external charger 50 is used to charge (or recharge) the IPG's battery 26. Similarly to the external controller 12, the coil 17′ is energized with an AC current to create a magnetic field 29. This magnetic field 29 induces a current in the charging coil 18 within the IPG 100, which current is rectified to DC levels, and used to recharge the battery 26, as explained further below. The external charger 50 will generally have many of the same basic components as the external controller 12, and therefore is labeled similar element numerals, denoted with prime symbols. However, while sufficient for purposes of this disclosure to view the external controller 12 and charger 50 as having generally similar components, one skilled in the art will realize that external controllers 12 and chargers 50 will have pertinent differences as dictated by their respective functions.
Inductive transmission of data or power can occur transcutaneously, i.e., through the patient's tissue 25, making it particular useful in a medical implantable device system. During the transmission of data or power, the coils 13 and 17, or 18 and 17′, preferably lie along a common axis in planes that are parallel. Such an orientation between the coils will generally improve the coupling between them, but deviation from ideal orientations can still result in reliable data or power transfer.
Further details concerning the communication circuitry in the external controller 12, the external charger 50, and the IPG 100 are shown in FIG. 3. As shown, the external controller 12 and the IPG 100 respectively contain modulation and demodulation circuitry coupled to their coils 17 and 13 for communicating data between them. When data 170 is to be sent from the external controller 12 to the IPG 100, the data is modulated (e.g., encoded) using modulation circuitry 120 in the external controller. On the receiving side, this data 170 is demodulated (e.g., decoded) using demodulation circuitry 125 in the IPG 100. Similarly, when data 172 is to be sent from the IPG 100 to the external controller 12, the data is modulated using modulation circuitry 124 in the IPG. On the receiving side, this data 172 is demodulated using demodulation circuitry 121 in the external controller 12. As mentioned above, one modulation protocol operable in the respective modulation and demodulation circuit blocks 120, 121, 124, and 125 is is FSK, and the details of such circuitry are well known.
The external charger 50 likewise has a two-way communication with the IPG 100, although some differences exist due to the fact that communication from the charger 50 to the IPG 100 generally communicates only unmodulated power 174, not modulated data. Communication of such power 174 occurs using charging circuitry 122 to energize coil 17′. As mentioned above, such power 174 is received at the IPG's charging coil 18, and converted to a DC level using a rectifier circuit 132. This rectified power is then sent to the IPG's battery 26, perhaps via charging/protection circuitry 134 that generally monitors and controls the battery charging process.
The IPG 100 can also communicate data 176 back to the external charger 50. Such back telemetry occurs using modulation circuitry 126. Modulation circuitry 126 receives data to be transmitted back to the external charger 50 from the IPG's microcontroller 150, and then uses that data to modulate the impedance of the charging coil 18. In the illustration shown, impedance is modulated via control of a load transistor 130, with the transistor's on-resistance providing the necessary modulation. This change in impedance is reflected back to coil 17′ in the external charger 50, which interprets the reflection at demodulation circuitry 123 to recover the transmitted data. This means of transmitting data from the IPG 100 to the external charger 50 is known as Load Shift Keying (LSK), and is useful to communicate data relevant during charging of the battery 26 in the IPG 100, such as the capacity of the battery, whether charging is complete and the external charger can cease, and other pertinent charging variables.
Also depicted in FIG. 3 is error code circuitry 140 useful in identifying particular failure modes in the IPG 100. The error code circuitry 140 monitors various voltages, interrupt signals, or other indicators 141 within the IPG 100. Through application of its logic, error code circuitry 140 generates an error code (usually numeric) corresponding to the particular failure mode. Because these error codes may be of importance to the patient, the patient's clinician, or the manufacturer of the IPG system, they are typically sent as data 172 from the IPG 100 to the external controller 12. Error code circuitry 140 may comprise a portion of the IPG's microprocessor 150, but is shown as a separate block for simplicity. The error code received at the external controller 12 may be sent to the external controller's user interface 74 for interpretation by the patient, clinician, or manufacturer.
Reporting of IPG error codes external to the patient is of great benefit to understanding, and perhaps fixing, problems with an IPG. As regards fixing such errors, particular error codes may suggest a problem with the software or stimulation program operating in the IPG. If such error codes are known, new software or stimulation programs can perhaps be sent to the IPG to fix the error. Even if a particular error is not immediately fixable, reporting of the error codes is still important to provide analysis of the particular failure involved. Such failure may indicate, for example, whether the IPG 100 can be fixed using extraordinary means (such as through the application of special manufacturer commands), whether the IPG 100 needs to be explanted from the patient, etc. Knowledge of the failure can also assist the manufacture of the IPG system to design a more robust system: without knowledge of particular failure modes, the manufacture may have to embark on complicated and time-consuming failure analysis of the system.
Unfortunately, the inventors have noticed that external reporting of error codes is not always possible. Many times, the inability to report such error codes from the IPG 100 results from failure modes so fundamental that the relevant communication circuitry in the IPG 100—such as the error code circuitry 140, the microcontroller 150, the modulation circuitry 124, etc.—cannot function to communicate the error code to the external controller 12. Such fundamental failure modes may result from improper initialization of the IPG 100. Initialization of the IPG 100 begins with the execution of the microcontroller 150 of “boot up” instructions stored in initialization logic 132. Such an initialization procedure is typically implemented when the IPG 100 recovers from a power down condition, for example, when the battery 26 has become so depleted that the IPG 100 enters a power-down mode or simply can no longer function. The initialization logic 132 may comprise instructions stored within the microcontroller 150, but is shown as a separate block for simplicity. The modulation 124/demodulation 125 circuitry in the IPG 100 may also require initialization, such as tuning or enablement, to function appropriately.
If a fundamental error occurs during initialization, or even after initialization, it may be impossible for the IPG 100 to telemeter error codes outside of the IPG. As a result, the patient, clinician, or manufacture may know nothing about the particular error involved, which inhibits taking any corrective action. The result might be that IPG 100 has to be explanted from the patient, which is painful and inconvenient, and therefore desirable only as a last resort. Such explant is regrettable if the fundamental error could be known, and perhaps fixed. As concerns manufacture of the IPG system, knowledge of fundamental errors greatly assist in failure analysis, which could allow the manufacture to improve the reliably of the IPG system's design. The art of implantable medical devices would benefit from an improved ability to externalize IPG errors, and this disclosure presents solutions.